The Mechanics of Breathing

SBI3U

Mechanics of Breathing

Breathing

• Inspiration: the act of taking air INTO the lungs, occurs when pressure inside the lungs is LOWER than pressure outside the lungs (i.e. atmospheric pressure)

• Expiration: the act of breathing OUT, occurs when pressure inside the lungs is GREATER than pressure outside the lungs (atmospheric)

Breathing Movements

• The body uses muscles to change the VOLUME of the thoracic cavity.

• This alters the PRESSURE inside the lungs• An increase in volume = decrease in pressure

(and vice versa)

Respiratory Muscles• Diaphragm: dome shaped

sheet of muscle separating thoracic and abdominal cavities.

• Intercostal muscles: muscles of the ribcage– External intercostals: outer

surface, pull ribs up– Internal intercostals: inner

surface, pull ribs down

Mechanics of INSPIRATION• Diaphragm CONTRACTS and FLATTENS (moves downwards)• Intercostals CONTRACT and move ribcage UPWARDS• Pleural membrane pulls on lungs• Result: – Lung volume:INCREASED– Pressure inside the lungs:DECREASED– AIR MOVES IN

Mechanics of EXPIRATION• Diaphragm RELAXES and RETURNS to DOME shape• Intercostals RELAX and move ribcage DOWNWARDS• Pleural Membrane no longer pulling on lungs• Result:

– Lung volume:DECREASED– Pressure inside the lungs:INCREASES– AIR MOVES OUT

• *Internal intercostals can pull ribs in further to force exhalation

Respiration and Gas Exchange• Once inside the lungs, air is exchanged with the gases

in the bloodstream. • External Respiration: The exchange of O2 and CO2

between air and blood (occurs in the lungs).• The alveoli are surrounded by tiny blood vessels

(capillaries); both have walls that are only a single cell layer thick to allow for diffusion of gases.

Respiration and Gas Exchange• the gases are exchanged due to differences in CONCENTRATION.– O2 in inhaled air > O2 in blood of capillaries in lungs.– CO2 in inhaled air < CO2 in blood of capillaries in lungs.

• So in external respiration, – O2 diffuses from the alveoli to the capillaries and – CO2 diffuses from the capillaries to the alveoli.

Respiration and Gas Exchange• Once in the bloodstream, oxygen travels throughout

the body.

• Internal Respiration: The exchange of O2 and CO2 between blood and the cells of the surrounding tissue (occurs in the body tissues).

• As blood passes body cells O2 diffuses from the capillaries to the tissue and CO2 diffuses from the tissue to the capillaries.

Lung Capacities• The full capacity of your lungs is not used up under

normal conditions - consider yawning, or blowing out a candle, or exercising.

• A spirometer is used to measure lung capacities and produces a spirograph

Lung Capacities

• Tidal Volume: volume of air inhaled and exhaled in a normal breathing movement

Lung Capacities

• Inspiratory Reserve Volume: the additional volume of air that can be taken in, beyond a regular or tidal inhalation.

• Inspiratory Capacity: total volume of air that can be taken in – (TV + IRV)

IRV

Lung Capacities

• Expiratory Reserve Volume: the additional volume that can be forced out of lungs

• Vital Capacity: the total volume of gas that can be moved in or out of the lungs– TV + IRV + ERV = VC

ERV

IRV

Lung Capacities

• Residual Volume: the amount of gas that remains in the lungs and passageways of the respiratory system even after full exhalation (prevents collapse, no value for gas exchange)